erratic voltage on my 2008 ST - BMW F800 Riders Forum & Registry



Remove this advertisement by REGISTERING.

Results 1 to 10 of 10
  1. #1
    Points: 1,556, Level: 23

    Real Name
    Noel
    Location
    Brisbane Australia
    Joined
    Nov 2018
    Online
    1 Day Ago
    Posts
    16 / 0 / 0 / 0
    I have blown two low beam headlamp bulbs over the last couple of month so decided to check if over-voltage may have been the issue (potential spikes or such)
    Sure enough, on testing with a multimeter the static voltage was 13 volts at the battery but when starting the bike and running up the revs a little I found the multimeter was fluctuating with intermittent spikes well above the acceptable 15 volts, perhaps momentary spikes above 20 volts
    My first thoughts were that it could be a faulty regulator / rectifier so just go and buy a new one. But then I know nothing about alternators other than they do have brushes in them that can wear out? My machine has done close on 40,000 kms so maybe they are in need of changing? Or could it be as simple as squirt some electrical contact cleaner into the wiring plug / socket and try the voltage test again?
    I don't mind replacing the odd lamp but some of the electronics on board go way beyond that for replacement so I am reluctant to just fiddle without some guidance if there is a knowledge base out there that can help? I guess the lamps blowing were the "canary in the coal mine" sending me a message - everything else was going ok but now I do have a warning on the dash.
    Any advice welcome

  2. Remove Advertisements
    F800Riders.org
    Advertisements
     

  3. #2
    Points: 749, Level: 14

    Real Name
    Max
    Location
    Southland, New Zealand
    Joined
    Mar 2020
    Online
    12 Hours Ago
    Posts
    17 / 0 / 0 / 0
    Motorcycle
    '08 F800 ST
    Noel

    Do check the battery terminals too - intermittent on them will make the charge voltage go all over the place, but would probably guess the reg/rect isn't doing its 'short to ground' properly to limit the output voltage ... the F800s have a permanent magnet alternator, so the strength of the magnet can't be controlled like a car alternator (eg ones with brushes), the output is 'always on' full blast so at higher RPMs/ light load the standard reg/rect momentarily shorts the output to ground so the excess gets dissipated as heat in the stator windings (have a search for stator failures).

    If you do go looking for another reg-rect would not suggest staying with a BMW unit - upgrade to a more modern MOSFET or 'series' regulator while you're in there anyway. Have a search for SH775, you'll find a lot of info around series regs and why they're supposed to be better.

    HTH

    Max

  4. Likes Oldman11 liked this post
  5. #3
    Runmyownlife's Avatar
    Points: 14,839, Level: 83

    Real Name
    Andrew
    Location
    Calgary, Alberta
    Joined
    Feb 2017
    Online
    1 Minute Ago
    Posts
    1,041 / 0 / 0 / 0
    Motorcycle
    '08 F800 ST
    Motorcycle
    '08 F800 ST
    I agree with Max regarding the rectifier/regulator. The regulator/rectifier is what limits voltage output. Too high is a sure sign that it has a problem.

    The stator works in unison and so replacing one means you should replace both. (And neither is expensive for the task they perform.) It's a very DIY project as no mechanical ability required - just patience.

    https://f800riders.org/forum/showthr...ator-rectifier

    As you are handy with a multi-meter, you can conduct a stator test. Follow the wires coming out of right side cover near your foot. These will lead to a connector. Notice the three yellow wires?

    There are three primary wires coming from the stator yielding AC voltage. Set the meter to AC and you should have 40-80 volts AC between each of the three phases:

    Y1...Y2....Y3

    Measure between y1 and y2, then y2 and y3 and then y3 and y1. At idle is fine. If any of those three legs don`t yield AC then the stator is toast.

    Now check for continuity. Turn the bike off. Use same 3 leads as measuring the AC voltage. This time the plug is disconnected (squeeze the sides of the connector.)

    Any open measurement is bad as you test between y1 and y2, y2 and y3, etc. Those should be about 0.5 ohms. If they are open that means that circuit is bad. The take each of the legs and measure to ground. No continuity is good. You want an open circuit here. If you don`t that means that part of that coil is short circuited to ground.


    Over voltage is a regulator issue, not a stator issue but they work as a team. Failure in one usually means a problem has occurred in the other, or the other is substantially weakened/damaged by the fault. It's all about voltage and heat between these two - very powerful forces when things go wrong.


    Credit to ADVRider forum member ebrabaek.
    Concrete remains undefeated. 

  6. Likes Oldman11 liked this post
  7. Remove Advertisements
    F800Riders.org
    Advertisements
     

  8. #4
    Points: 1,556, Level: 23

    Real Name
    Noel
    Location
    Brisbane Australia
    Joined
    Nov 2018
    Online
    1 Day Ago
    Posts
    16 / 0 / 0 / 0
    Thanks to both of you, I like the sound of the modification, had already seen elsewhere that the SH775 was well recommended
    As an Ex Kiwi myself who has also spent a couple of years (long time ago) in Alberta I feel among friends
    Question for Max, you understanding the "extra" cost we pay down under for anything we import: where did you buy your parts and what was the approximate cost?
    I am in my 70's, retired, so have time on my hands though I will dislike parking up the bike for an extended period if I have to wait for parts from the northern hemisphere.
    Much better if I can purchase in Aussie (or NZ if required) just to hurry things along.
    I also had a question about the plugs/ sockets required for any modification - how hard are they to come by and where to buy them?
    My Rec/Reg has the number SH541G-12 which when I searched would indicate it came off a Honda perhaps?
    And by the charge state of the battery it would "appear" to my unlearned self that the Stator is/was still doing its job?

  9. #5
    Points: 1,556, Level: 23

    Real Name
    Noel
    Location
    Brisbane Australia
    Joined
    Nov 2018
    Online
    1 Day Ago
    Posts
    16 / 0 / 0 / 0
    Update: I just checked on line and both RR and stator can be purchased from right here in Aussie - Looks like $756.85
    Oh well, its only money, and if I don't spend it, the "kids" will
    I note the connectors look the same as original, nothing to modify with the Mosfet SH775

  10. #6
    Runmyownlife's Avatar
    Points: 14,839, Level: 83

    Real Name
    Andrew
    Location
    Calgary, Alberta
    Joined
    Feb 2017
    Online
    1 Minute Ago
    Posts
    1,041 / 0 / 0 / 0
    Motorcycle
    '08 F800 ST
    Motorcycle
    '08 F800 ST
    Glad you've got it sorted. And what a surprise to hear you've lived in Alberta! You may be pleased to know Aussies remain well represented here, particularly in Banff and Jasper.

    I've been to Perth, Melbourne and Sydney. Next time, I'll load my suitcase with motorcycle parts. Quite a price difference.
    Concrete remains undefeated. 

  11. #7
    ccramerusc's Avatar
    Points: 8,695, Level: 64

    Real Name
    Cramer
    Location
    Milwaukee, WI
    Joined
    Jun 2013
    Online
    9 Hours Ago
    Posts
    726 / 0 / 0 / 6
    Motorcycle
    '08 F800ST
    I would agree that the charge state of the battery indicates that the stator is fine. You can do the Y1, Y2, Y3 test as stated above to confirm this. Assuming that is the case, you only need a new R/R. I picked up a used Shindengen SH775 a couple years ago for $100 US on ebay. It bolts right on in 2 minutes, but did require some wiring because the connectors were different. I've replaced my stator 4 times over the past 7 years. It is not hard to do, but you do need a new gasket when reinstalling.

    Sent from my SAMSUNG-SM-G891A using Tapatalk
    08' F800ST- side panniers & Shad SH45 top case, Russell Day Long seat, MRA Vario Windscreen, SW Motech crash bars, ZTechnik exhaust, PC-8 fuseblock, Stebel Nautilus horn, Throttlemeister throttle lock, SW Motech handlebar risers, LED fog lights, highway pegs 

  12. #8
    Points: 1,556, Level: 23

    Real Name
    Noel
    Location
    Brisbane Australia
    Joined
    Nov 2018
    Online
    1 Day Ago
    Posts
    16 / 0 / 0 / 0
    Steep learning curve here for me Guys, I am a "can do" sort of person, having done a full restoration on a now trophy winning '69 H1 hence my comment about the brushes (which it had)
    Cramer, I am shocked to read the number of stators you have replaced, surely they must be of poor quality, but Max's thoughts about replacing both items at the same time and going the way of Mosfet R/R would have considerable logic to it?
    At the prices we pay for this product it hurts but it would hurt a dam sight more if I had to do it all again in 18 months!
    I will do a stator test in any event, now that I know how, but the logic that it may be damaged due to over heating (and fail down the track) makes a good argument for replacement.
    A "tow" back home from some distant location would quickly swallow up any short term savings and then some
    I do appreciate each and every comment because it gives balance to the advice so thank you one and all

  13. #9
    ccramerusc's Avatar
    Points: 8,695, Level: 64

    Real Name
    Cramer
    Location
    Milwaukee, WI
    Joined
    Jun 2013
    Online
    9 Hours Ago
    Posts
    726 / 0 / 0 / 6
    Motorcycle
    '08 F800ST
    My fist replacement was done by a BMW shop during a road trip 1000 miles from home. Cost me $1200! My second and 3rd replacement I did at home with cheap aftermarket parts (stators were about $200). My last one was a BMW part, at the same time that I swapped the R/R to a series style. Additionally, I changed the rotor to the newer design with more holes for oil cooling.

    The rotor is a point worth mentioning. Around 2010 they changed the rotor design to improve cooling. It's not easy to remove, but plenty of heat and an impact wrench on a M22X1.5 R.H. External Thread puller got it off.

    Hopefully I'll be good for a long time now that I have a new rotor, original brand stator and a series R/R.

    Sent from my SAMSUNG-SM-G891A using Tapatalk
    08' F800ST- side panniers & Shad SH45 top case, Russell Day Long seat, MRA Vario Windscreen, SW Motech crash bars, ZTechnik exhaust, PC-8 fuseblock, Stebel Nautilus horn, Throttlemeister throttle lock, SW Motech handlebar risers, LED fog lights, highway pegs 

  14. #10
    Points: 6,289, Level: 54

    Real Name
    Bob Cuttler
    Location
    Ridge, NY
    Joined
    Aug 2013
    Online
    3 Days Ago
    Posts
    48 / 0 / 0 / 2
    [QUOTE=Oldman11;2863955]I have blown two low beam headlamp bulbs over the last couple of month
    =======================================
    I've got a 2013 GT with some 75,000 miles on it. I think it's fair to say i have never gone 6 months straight
    with both bulbs lit. One after another they blow out. I've installed a high output twin LED light, so it's not
    an issue anymore. For some reason I never had both bulbs out at the same time. It never occurred to me
    to check on charging voltage, but the first time a bulb blew out twice in a couple of months it was still under the
    warranty and I brought back to the dealer to look for a problem. It would hope the dealer mech. would be well
    trained enough to have checked the voltage if that was a possible cause. FWIW I had a Honda ST1100 that
    regularly charged at over 15 volts, usually 15.2, and never blew any H4 bulbs. So i've never found the problem
    and I'm currently riding with the high beam out, but like I say I now rely on the LEDs I installed.

    Bob

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •